The invention relates to a pump nozzle for fuel injection in internal combustion engines, including a pump piston comprising two parts, namely of a mechanically driven transport piston and of a coaxial slave piston working in the same pump cylinder. The transport piston and the slave piston enclose between them an equalizing chamber to which a supply bore carries a fluid of a low pressure. The supply bore is closable, after the onset of delivery, by means of the edge of the transport piston near the equalizing chamber. The pump nozzle includes a relief bore which communicates with the pump cylinder, and which, in order to terminate the pump motion of the slave piston, is openable by means of the edge of the slave piston nearest to the equalizing chamber. A pump working chamber defined by the end of the slave piston remote from the equalizing chamber, receives a predetermined quantity of pre-loaded fuel during the pauses between injections via a filler line equipped with a check valve. A pressure line leads to the pressure chamber of the nozzle.
In a familiar pump nozzle of this kind, fuel is injected into the internal combustion engine even after the intended termination of the injection operation, as a result of the dynamic relationships within the pump working chamber. This protraction of the injection termination results in a deterioration of the exhaust gas value, quite apart from a greater fuel consumption and detrimental noise generation.